“Nothing But a Man” is one of the two best movies ever made about black life in America. The other is Charles Burnett’s “Killer of Sheep,” from 1977, an oblique, black-and-white daydream of life in South Los Angeles. “Nothing But a Man” was directed and co-written by Michael Roemer and released in 1964 and also filmed in black and white. But it unfolds with a clear-eyed realism that can’t afford the luxury of Burnett’s disorienting magic.

Delicately but not unsparingly, Roemer’s movie, which screens at the Harvard Film Archive through Jan. 20, tells the story of a handsome railroad worker named Duff (Ivan Dixon), who meets a schoolteacher named Josie (Abbey Lincoln) and leaves his itinerant section crew to settle down with her in a modest country shack. But romance is elusive and headaches steady. Duff takes a labor job and isn’t amused by the pointed joshing of a lone white co-worker. The other men tolerate it because it is, they feel, their lot in life: turning the other cheek.

Duff’s suggestion of solidarity is too radical for them. Their white manager gets wind and asks Duff to tell the rest of the crew he wasn’t serious about any sort of union. He quits instead and earns a reputation as the sort of trouble a white boss wouldn’t want, recharacterizing what it means to be blacklisted. He’s left with menial work, wavering enthusiasm for his domestic life, and too much time to consider what he means to his estranged young son and what his estranged alcoholic father (Julius Harris) means to him.

I’m not a fan of the human condition as a term. Often it doesn’t specify what the condition is or it’s deployed to impart a belief that life is suffering. But for a white director in 1964 to send his camera into black homes and stare into black faces and report the condition of being human still feels like a revelation. That Roemer did so with intelligent, sentient, and imperfect characters played by professional actors gives the movie’s transparent documentary style its simmering dramatic shape.

The acting is a crucial element of the film’s resonance. Roemer didn’t find these people on the street. They were professional artists, and when the camera gazes at them in any of the film’s many close-ups they give something back. Lincoln’s great jazz career was already underway when Roemer cast her. Harris, who is astounding, began his acting career in this film. A young Yaphet Kotto plays one of Duff’s section crew members. Gloria Foster, who plays the tense, tired girlfriend of Duff’s deteriorating old man, would become famous as the Oracle in the “Matrix” movies. And Dixon became Kinch on “Hogan’s Heroes” and had a long career directing television series. He was also a civil rights activist. And the film lands Duff in this transitional moment between black passivity and black empowerment. He doesn’t know how to be the Negro who simply smiles off racism, the way his co-workers recommend he do, and it starts to drive him crazy. It’s as if he can feel progress and is exasperated by its moseying pace.

Most American movies about blacks and the working poor would cast a pitying eye on Duff, Josie, their family and friends and call that sympathy. They would find a way to sweeten the bitterness with soundstages and uplift, with Hollywood. But Roemer and his camera (operated by his co-writer, Robert M. Young) get so far into the lives of these characters that you never feel self-defeat or woe — or that’s not all you feel.

Roemer wasn’t just any white director. He was a German Jew whose family was financially crippled by Nazi policies. He was lucky enough to escape the Holocaust as part of the Kindertransport rescue mission and make it to the United States. When he looks into the faces of Dixon and Kotto and Foster, it’s not the guilt of slavery and American racism he’s seeing. It’s not a wish for atonement or catharsis. With melancholic empathy, Roemer simply sees himself.

I took a documentary film survey with him at Yale, where he’s taught for years. He’s 85 now. He showed all the great movies, including one of his own, “Dying.” But he was really proud of the one he made in 1964. I don’t think any of us could appreciate the movie at the time. We were indifferent to it. We were also young. Some of us shrugged at Alain Resnais’s “Night and Fog’’ and Frederick Wiseman’s movies, too. I’ve always regretted not telling him that he’d made an enduring milestone. He knew his achievement was special. I think he also knew that someday, his frivolous students would figure that out.